The present invention relates generally to catheters systems. In particular, the present invention is directed to a drive coupling for a catheter assembly that provides for the controlled longitudinal movement of an elongate elementxe2x80x94such as a rotatable catheter core with an operative element, for example an ultrasonic transducer or an optical fiber imaging device, at its distal end, or a drive cable with an arthrectomy cutter at its distal endxe2x80x94housed within a sheath positioned within a patient.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both peripheral blood vessels which feed the limbs of the body and the coronary vessels which feed the heart. When the deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person""s health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of atheroma, and other devices that are pushed or pulled along or through a deposit, such as arthrectomy where a blade or cutting bit is used to sever and remove the atheroma, spark gap reduction in which an electrical spark burns through the plaque, laser angioplasty where laser energy is used to ablate at least a portion of the atheroma, and opening of vessels through the use of stents.
Two major difficulties in using such devices are maintaining a constant translational rate for the device and obtaining images of and information on the region of the blood vessel to be treated. Several imaging techniques have been proposed. Catheters incorporating mechanical rotation of ultrasonic transducers for imaging are disclosed in U.S. Pat. Nos. 4,794,931; 5,000,185; 5,049,130; and 5,024,234. These catheters scan in a plane normal to the catheter axis. Catheters employing phased array imaging systems are disclosed in U.S. Pat. Nos. 4,841,977 and 4,917,097. Catheters employing fiber optic imaging components are also known.
Generally deposits extend some longitudinal distance along the length of a vessel. To view different portions of the deposit a physician typically moves a handle attached to a proximal end of the imaging catheter along the vessel, for example, by pushing or pulling the catheter.
Imaging using computer-assisted reconstruction algorithms enables physicians to view a representation of the patient""s interior intravascular structures in two or three dimensions (i.e., so-called three-dimensional or longitudinal view reconstruction). In this connection, image reconstruction algorithms typically employ data-averaging techniques which assume that the intravascular structure between an adjacent pair of data samples will simply be an average of each such data sample. Thus, the algorithms use graphical xe2x80x9cfill inxe2x80x9d techniques to depict a selected section of a patient""s vascular system under investigation. Of course, if data samples are not sufficiently closely spaced, then lesions and/or other vessel abnormalities may in fact remain undetected (i.e., since they might lie between a pair of data samples and thereby be xe2x80x9cmaskedxe2x80x9d by the image reconstruction algorithms mentioned previously).
Even with the most skilled physician, it is practically impossible to manually exercise sufficiently slow constant rate longitudinal translation of the ultrasound imaging device (which thereby provides for a precisely known separation distance between adjacent data samples). In addition, with manual translation, the physician must manipulate the translation device while observing the conventional two-dimensional sectional images. This division of the physician""s attention and difficulty in providing a sufficiently slow constant translation rate can result in some diagnostic information being missed. To minimize the risk that diagnostic information is missed, it is necessary to lengthen the imaging scan time which may be stressful to the patient. Similarly, it is difficult for physicians to manually control the translational rate of arthrectomy catheters and other interventional devices that are longitudinally advanced and retracted through blood vessel and other body lumens.
U.S. Pat. No. 5,485,486 discloses an ultrasound imaging transducer which is capable of being translated longitudinally within a section of a patient""s vascular system at a precise constant rate through the use of a longitudinal translation assembly. The longitudinal translation assembly moves the entire rotary drive assembly to provide the desired longitudinal movement of the transducer. Such an ability enables a series of precisely separated data samples to be obtained thereby minimizing (if not eliminating) distorted and/or inaccurate reconstructions of the ultrasonically scanned vessel section (i.e., since a greater number of more closely spaced data samples can reliably be obtained). Also, such an assembly can be operated in a xe2x80x9chands-offxe2x80x9d manner which allows the physician to devote his or her attention entirely to the real-time images with the assurance that all sections of the vessel are displayed. While such a longitudinal translation assembly can work well, it is relatively large, bulky and heavy; it is expensive; and it is cumbersome to set up, in part because the rotary drive and longitudinal translation assemblies are wrapped in separate sterile drapes or barriers (plastic bags) for sterility.
One of the disadvantages with some conventional pullback systems is separate modules are used to provide the rotational and translational movement. These modules require the use of sterile barriers about each. Also, some prior art pullback systems lack the capability to permit the user to manually translate the catheter core to preposition the operative element along the distal end of the catheter core.
The present invention is directed to a driven catheter system including rotational and translational drive coupling as part of a catheter assembly. The invention eliminates the need for a sled as is used with many conventional catheter pullback units. User set up is greatly simplified with the invention. The catheter assembly is typically a disposable unit and is thus supplied to the user in a sterile condition so only a single sterile drape about a motor drive unit is needed.
The driven catheter system includes broadly a driven catheter assembly coupled to a control unit. The driven catheter assembly includes the motor drive unit and the catheter assembly mounted thereto. The catheter assembly includes a catheter extending from the rotational and translational drive coupling. The catheter includes a sheath and a core slidably housed within the sheath, the proximal end of the sheath being mounted to the housing of the drive coupling. The drive coupling includes an elongate rotary drive element, defining a first longitudinal drive path, mounted to the housing for rotation about a longitudinal axis. A termination element couples the proximal end of the core to the rotary drive element for longitudinal movement along the first longitudinal drive path. The termination element is also mounted to the rotary drive element for of the termination element and the core therewith by the rotary drive element. A bearing has a first part coupled to the termination member. The bearing also has a second part, the first and second parts being freely rotatable relative to one another. A longitudinal driver is mounted to the housing and has a longitudinal drive element coupled to the second part of the bearing. The longitudinal drive element is movable along a second longitudinal drive path. Accordingly, rotation of the rotary drive element rotates the termination element and the proximal end of the core therewith about the longitudinal axis. Longitudinal movement of the longitudinal drive element translates the bearing parallel to the longitudinal drive path; this causes the termination element and the proximal end of the core therewith to be translated along the first longitudinal drive path.
The rotary drive element preferably has a hollow interior which defines the first longitudinal drive path. A slot, opening into the hollow interior, can be provided to be oriented parallel to the longitudinal drive path. The first part of the bearing, typically the inner race of the bearing, is preferably connected to the termination member through the slot. The longitudinal drive element could be provided by a number of different drive structures, such as a continuous belt, a lead screw or worm drive. In a preferred embodiment a continuous loop drive belt is used. The drive belt is driven through a drive pulley. The drive pulley is preferably driven through a pair of bevel gears. A flexible data/signal line, in the preferred embodiment, extends between the termination element at the proximal end of the core and a data/signal terminal carried by the housing of the drive coupling. The data/signal terminal may be a separate terminal but is preferably part of a dual data/signal-rotary drive connector. The dual connector provides the necessary data/signal connection and also the rotary drive connection for the rotary drive element.
The motor drive unit includes first and second rotary drive outputs which are coupled to the elongate rotary drive element and the longitudinal driver, respectively. The motor drive unit preferably includes first and second drive trains each having driving and driven ends. The driving ends terminate at the first and second rotary drive outputs. The second drive train couples the second rotary drive outputs with a drive source, typically an electric motor. A clutch-type element and a movement indicator, such as an optical encoder, may be used along the second drive train. The optical encoder is preferably positioned between the clutch type element and the second rotary drive output. Provision of the clutch-type element permits a user to physically disengage the longitudinal driver from the drive source so that the termination element and the core therewith can be manually translated within the sheath without the drag which would otherwise be created by the drive source. The preferred position of the movement indicator ensures that the longitudinal position of the core is continuously updated even when the core is being manually translated.
Other features and advantages of the present invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.